The present invention is directed to a sensor, for determining the oxygen content of exhaust gases produced by internal combustion engines to. The German Published Unexamined Application No. DE-OS 27 02 432 discloses a Lambda probe type gas sensor of this type, for example, where the reference air is introduced via a connecting cable into the housing, and the cavities disposed in the connecting cable insulation are not always sufficient to conduct enough reference air into the interior of the sensor's housing. One has to consider here that this reference air must be renewed at regular intervals, i.e., it must be coupled to the ambient air. On the other hand, to achieve unbiased measuring results, it is absolutely necessary that the reference air not come in contact with the exhaust gas to be measured, or e.g., with dirt, water, oil or gasoline from the ambient air. According to today's state of technological development, reference air is coupled to ambient air by way of a cable core, i.e., by way of the inner stranded conductor of the measuring cable, e.g., from the control unit. When the cable is lead through the measuring probe, the insulation sheath of the measuring cable must be sealed off absolutely imperviously. This process of leading the cable through is quite complex, since it requires manufacturing and assembling various components. This complexity is reflected accordingly in the manufacturing costs.